Beryl
Beryl | |
---|---|
Chemical composition | Be3Al2(SiO3)6 Beryllium aluminum silicate |
Crystal system | Hexagonal |
Habit | Prismatic |
Cleavage | Very difficult in one direction, rarely seen |
Fracture | Conchoidal |
Hardness | 7.25-7.75 |
Optic nature | Uniaxial - |
Refractive index | 1.577-1.583 (+ or - 0.017) |
Birefringence | 0.005-0.009 |
Dispersion | Low, 0.014 |
Specific gravity | 2.72 (+0.18,- 0.05) |
Lustre | Vitreous to resinous |
Pleochroism | Weak to moderate |
Beryl is a beryllium aluminum silicate that occurs in every color of the rainbow. When green, it's an emerald. When blue, it's aquamarine. When pink, it's morganite. There is a raspberry red variety found in Utah called Bixbite. Yellow is heliodor and colorless is goshenite. There is a very rare and costly variety termed riesling beryl, that can be described as pale green colour, with a warm golden yellow flash. Two unusually dark blue types of beryl have been found as well, Maxixe beryl and True Blue beryl. Maxixe beryl fades with exposure to light, True Blue beryl does not. Beryl had been used as a physician's tool and gazing stone since ancient times. Those beliefs persist today. Beryl is metaphysically attributed with the ability to cure a number of intestinal and stomach ills, such as nausea, ulcers, and seasickness.
Contents
Characteristics
The optical and physical data of Beryl can vary between varieties and localities.
Beryl belongs to the Beryl Group (another member of the Beryl Group is Pezzottaite).
Genesis
Metamorphic rocks in pegmatites
Localities
Beryl is found in many localities, amongst them are Brazil, India, Africa, Columbia, Australia and Pakistan.
Habit
Prismatic with pyramidal and pinacoidal terminations. Often vertically striated.
Physical data
Moh's hardness: 7.25 - 7.75 (Emerald is brittle).
Specific gravity: 2.7 to 2.9, depending on variety.
Optical data
Refractive index: nε = 1.56 nω = 1.59, depending on variety.
Birefringence: 0.004 to 0.009, depending on variety.
Optical sign: Uniaxial negative.
Dispersion: low, 0.014
Diapheny
Transparent to translucent.
Colors
Beryl and all its varieties are allochromatic. Main coloring agents are given.
- Green (Emerald), colored by Chromium 3+
- Green (Vanadium Beryl), colored by Vanadium 3+
- Green (Green Beryl), colored by Ferric 3+ and ferrous 2+ Iron
- Green/Yellow (Reisling Beryl), unknown coloring agent
- Blue (Aquamarine), colored by Ferrous 2+ Iron
- Blue (Maxixe), colored by color centers
- Blue (True Blue), colored by Ferrous 2+ Iron (most likely)
- Pink (Morganite), colored by Manganese 2+
- Red (Bixbite), colored by Manganese 3+
- Yellow (Heliodor), colored by Ferrous 3+ Iron
- Colorless (Goshenite)